Nickel base superalloy and single crystal castings

ABSTRACT

Rhenium-bearing single crystal nickel base superalloy consisting essentially of, in weight %, about 12.5% to about 13.5% Cr, 9.0 to about 9.9% Co, about 4.7 to about 5.1% Ti, about 2.8 to about 3.2% Al, about 2.8 to about 4.3% W, about 1.4 to about 1.6% Mo, about 2.85 to about 3.1% Ta, about 1.0 to about 6.0% Re, about 0.08 to about 0.11% C, about 0.010 to about 0.015% B, up to about 0.15% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidental impurities.

This application claims the benefits and priority of Ser. No. 60/482,579filed Jun. 25, 2003.

FIELD OF THE INVENTION

The present invention relates to a nickel base superalloy and to singlecrystal castings, such as single crystal airfoil castings, made from thesuperalloy.

BACKGROUND OF THE INVENTION

Superalloys are widely used as castings in the gas turbine engineindustry for critical components, such as turbine airfoils includingblades and vanes, subjected to high temperatures and stress levels. Suchcritical components oftentimes are cast using well known directionalsolidification (DS) techniques that provide a single crystalmicrostructure or columnar grain microstructure to optimize propertiesin one or more directions.

Directional solidification casting techniques are well known wherein anickel base superalloy remelt ingot is vacuum induction remelted in acrucible in a casting furnace and poured into a ceramic investmentcluster mold disposed in the furnace having a plurality of moldcavities. During directional solidification, the superalloy melt issubjected to unidirectional heat removal in the mold cavities to producea columnar grain structure or single crystal in the event a crystalselector or seed crystal is incorporated in the mold cavities.Unidirectional heat removal can be effected by the well known moldwithdrawal technique wherein the melt-filled cluster mold on a chillplate is withdrawn from the casting furnace at a controlled rate.Alternately, a power down technique can be employed wherein inductioncoils disposed about the melt-filled cluster mold on the chill plate arede-energized in controlled sequence. Regardless of the DS castingtechnique employed, generally unidirectional heat removal is establishedin the melt in the mold cavities.

SUMMARY OF THE INVENTION

The present invention provides in one embodiment a nickel basesuperalloy consisting essentially of, in weight %, about 12.5% to about13.5% Cr, about 9.0 to about 9.9% Co, about 4.7 to about 5.1% Ti, about2.8 to about 3.2% Al, about 2.8 to about 4.3% W, about 1.4 to about 1.6%Mo, about 2.85% to about 3.1% Ta, about 1.0 to about 6.0% Re, about 0.08to about 0.11% C, about 0.010 to about 0.015% B, up to about 0.15% Nb,up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni andincidental impurities. A preferred range for the Re concentration isabout 2% to about 4% by weight.

A nickel base superalloy having a nominal composition pursuant to aparticular embodiment of the invention consists essentially of, byweight, about 13.0% Cr, about 9.0% Co, about 4.9% Ti, about 3.0% Al,about 3.0% W, about 1.5% Mo, about 2.95% Ta, about 3.0% Re, about 0.09%C, about 0.012% B, up to about 0.15% Nb, up to about 0.15% Hf, up toabout 0.003% Zr, and balance Ni and incidental impurities. Preferably,Nb, Hf, and Zr each are maintained at respective impurity levelconcentrations in the alloy.

The present invention provides in another embodiment a nickel basesuperalloy consisting essentially of, in weight %, about 9.5% to about14.0% Cr, about 7.0 to about 11.0% Co, about 3.0 to about 5.0% Ti, about3.0 to about 4.0% Al, about 3.0 to about 4.0% W, about 1.0 to about 2.5%Mo, about 1.0% to about 4.0% Ta, about 1.0 to about 6.0% Re, up to about0.25% C, up to about 0.015% B, up to about 1.0% Nb, up to about 0.15%Hf, up to about 0.003% Zr, and balance Ni and incidental impurities. Apreferred range for the Re concentration is about 2% to about 4% byweight. Preferably, Nb, Hf, and Zr each are maintained at respectiveimpurity level concentrations in the alloy.

Another nickel base superalloy having a nominal composition pursuant toa particular embodiment of the invention consists essentially of, byweight, about 11.75% Cr, about 9.0% Co, about 4.0% Ti, about 3.5% Al,about 3.5% W, about 1.75% Mo, about 2.5% Ta, about 3.0% Re, about 0.09%C, about 0.012% B, up to about 1.0% Nb, up to about 0.15% Hf, up toabout 0.003% Zr, and balance Ni and incidental impurities.

A nickel base superalloy pursuant to embodiments of the inventionpossesses improved castability and improved mechanical properties.

Other advantages, features, and embodiments of the present inventionwill become apparent from the following description.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph representing the Larson-Miller parameter for inventionalloys A and B pursuant to embodiments of the invention and forcomparison CompSX, CMSX-4, PWA 1484, and Rene'N5 nickel basesuperalloys.

FIG. 2 is a graph representing the Larson-Miller parameter for inventionalloy B pursuant to an embodiment of the invention and for comparisonCompSX nickel base superalloy.

FIG. 3 is a bar graph showing stress rupture life for invention alloys Aand B pursuant to embodiments of the invention and for comparison CompSxnickel base superalloy.

FIG. 4 is a bar graph representing the Larson-Miller parameter atdifferent stress levels for invention alloys A and B pursuant toembodiments of the invention and for comparison CompSX nickel basesuperalloy.

FIG. 5 is a graph of ultimate tensile strength (UTS) versus temperaturefor invention alloy A pursuant to an embodiment of the invention and forcomparison CompSX, CMSX-4, PWA 1484, and Rene'N5 nickel basesuperalloys.

FIG. 6 is a graph of 0.2% yield stress versus temperature for inventionalloy A pursuant to an embodiment of the invention and for comparisonCompSX, PWA 1484, and Rene'N5 nickel base superalloys.

FIG. 7 is a graph of percent elongation versus temperature for inventionalloy A pursuant to an embodiment of the invention and for comparisonCompSX, CMSX-4, PWA 1484, and Rene'N5 nickel base superalloys.

FIG. 8 is a graph of percent reduction in area versus temperature forinvention alloy A pursuant to an embodiment of the invention and forcomparison CompSX, CMSX-4, PWA 1484, and Rene'N5 nickel basesuperalloys.

DESCRIPTION OF THE INVENTION

The present invention provides a nickel base superalloy which is usefulin directional solidification processes to make gas turbine enginecomponents subjected to high temperatures and stress levels, such asturbine airfoils including blades and vanes, although the invention isnot limited to use in such processes or to make such components. Thenickel base superalloy is especially useful in directionalsolidification processes to make columnar grain castings or singlecrystal castings.

Pursuant to an embodiment of the invention, the nickel base superalloyconsists essentially of, in weight %, about 12.5% to about 13.5% Cr,about 9.0 to about 9.9% Co, about 4.7 to about 5.1% Ti, about 2.8 toabout 3.2% Al, about 2.8 to about 4.3% W, about 1.4 to about 1.6% Mo,about 2.85% to about 3.1% Ta, about 1.0 to about 6.0% Re, about 0.08 toabout 0.11% C, about 0.010 to about 0.015% B, up to about 0.15% Nb, upto about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidentalimpurities. Such nickel base superalloy typically will exhibit a PhaComp (N_(v)) value of about 2.37 or less.

The Pha Comp value corresponds to the electron vacany number (N_(v)),which is described in U.S. Pat. No. 6,054,096, the teachings of whichare incorporated herein by reference to this end. The N_(v) valuerepresents the propensity of the superalloy microstructure to bemicrostructurally unstable under elevated temperature and time serviceconditions where the instability relates to formation of brittleextraneous phases in the superalloy microstructure under the extendedservice conditions. Such extraneous phases are often referred to as TCP(topologically closed packed) phases, such as for example sigma phaseand mu phase.

The concentrations of Cr, Co, W, and Mo are closely controlled withinthe above ranges to achieve the above PhaC Comp (N_(v)) value so as toimprove microstructural stability of the superalloy in service atanticipated elevated temperatures and times experienced by airfoils in agas turbine engine.

The Re alloying element preferably is present in amount of about 2% toabout 4% by weight and more preferably about 3.0% Re. Re is present inthe superalloy to increase strength of single crystal castings made ofthe superalloy. Preferably, Nb, Hf, and Zr each are maintained atrespective impurity level concentrations in the alloy.

The invention contemplates a nickel base superalloy having a nominalcomposition that consists essentially of, by weight, about 13.0% Cr,about 9.0% Co, about 4.9% Ti, about 3.0% Al, about 3.0% W, about 1.5%Mo, about 2.95% Ta, about 3.0% Re, about 0.09% C, about 0.012% B, up toabout 0.15% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balanceNi and incidental impurities. Such nickel base superalloy typicallyexhibits a Pha Comp (N_(v)) value of about 2.37.

Pursuant to another embodiment of the invention, the nickel basesuperalloy consists essentially of, in weight %, about 9.5% to about14.0% Cr, about 7.0 to about 11.0% Co, about 3.0 to about 5.0% Ti, about3.0 to about 4.0% Al, about 3.0 to about 4.0% W, about 1.0 to about 2.5%Mo, about 1.0% to about 4.0% Ta, about 1.0 to about 6.0% Re, up to about0.25% C, up to about 0.015% B, up to about 1.0% Nb, up to about 0.15%Hf, up to about 0.003% Zr, and balance Ni and incidental impurities. Apreferred range for the Re concentration is about 2% to about 4% byweight. Preferably, Nb, Hf, and Zr each are maintained at respectiveimpurity level concentrations in the alloy.

The invention contemplates another nickel base superalloy having anominal composition pursuant to a particular embodiment of the inventionconsisting essentially of, by weight, about 11.75% Cr, about 9.0% Co,about 4.0% Ti, about 3.5% Al, about 3.5% W, about 1.75% Mo, about 2.5%Ta, about 3.0% Re, about 0.09% C, about 0.012% B, up to about 1.0% Nb,up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni andincidental impurities. Such nickel base superalloy typically exhibits aPha Comp (N_(v)) value of about 2.20.

The nickel base superalloys pursuant to the invention will beproduction-castable from the standpoint that it can be cast into complexsingle crystal shapes including solid and/or hollow components, such assingle crystal gas turbine engine airfoils including blades and vanes.The castings will be generally free from casting scale that is formed onsingle crystal castings made from low carbon single crystal nickel basesuperalloys.

Single crystal test bars for mechanical property testing were cast usinga superalloy pursuant to an embodiment of the invention having thenominal composition, in weight %, 13.3% Cr, 9.1% Co, 4.83% Ti, 3.06% Al,2.99% W, 1.49% Mo, 2.97% Ta, 2.98% Re, 0.087% C, 0.012% B, 0.0012% Nb,0.0007% Hf, 0.0001% Zr, and balance Ni and incidental impurities(designated invention alloy A).

Additional single crystal test bars for mechanical property testing werecast using a superalloy pursuant to an embodiment of the inventionhaving the nominal composition, in weight %, 13.9% Cr, 9.4% Co, 4.9% Ti,3.0% Al, 3.85% W, 1.58% Mo, 2.94% Ta, 0.09% C, 0.012% B, LAP Zr, LAP Nb,LAP Hf, and balance Ni and incidental impurities wherein LAP is low aspossible impurity level (designated invention alloy B).

The single crystal test bars were made by casting the above-describedinvention alloys A and B at a temperature of alloy melting point plus350-400 degrees F. into a shell mold preheated to 2750-2850 degrees F.The superalloy test bars were solidified as single crystal test barsusing the conventional directional solidification withdrawal techniqueand a pigtail crystal selector in the shell molds. Directionalsolidification processes for making single crystal castings aredescribed in U.S. Pat. Nos. 3,700,023; 3,763,926; and 4,190,094. Thesolidified as-cast test bars of both invention alloys A and B weresubjected to a primary aging heat treatment at 2050 degrees F. for 2hours, gas fan cooled at greater than 75 degrees F./minute to a finalaging heat treatment at 1550 degrees F. for 16 hours and then gas fancooled at greater than 25 degrees F./minute to room temperature formechanical property testing.

Similar single crystal comparison test bars were made from a knowncomparison CompSX nickel base superalloy, PWA 1484 nickel basesuperalloy, N5 nickel base superalloy, and CMSX-4 nickel base superalloyalso using the conventional directional solidification withdrawaltechnique. These nickel base superalloys are in commercial use in themanufacture of single crystal airfoil castings for use in gas turbineengines. The CompSX nickel base superalloy is described in U.S. Pat. No.6,416,596; the PWA 1484 nickel base superalloy is described in U.S. Pat.No. 4,719,080; the N5 nickel base superalloy is described in U.S. Pat.No. 6,074,602; and the CMSX-4 nickel base superalloy is described inU.S. Pat. No. 4,643,782. The CMSX-4 nickel base superalloy limits carbonto a maximum of 60 ppm by weight. The CompSX nickel base superalloy usedin the mechanical property testing had a nominal composition, in weight%, 13.9% Cr, 9.4% Co, 4.9% Ti, 3.0% Al, 3.85% W, 1.58% Mo, 2.94% Ta,0.09% C, 0.012% B, less than 50 ppm by weight Zr, LAP Nb, LAP Hf, andbalance Ni and incidental impurities wherein LAP is low as possibleimpurity level. The CompSX test bars were single crystal cast and heattreated in the same manner as the invention alloy A and B test bars.

The test bars were tested at different elevated temperatures for stressrupture resistance using test procedure ASTM E139 and tensile tested atroom temperature and elevated temperatures for ultimate tensile strength(UTS), 0.2% yield strength, percent elongation, and reduction in areausing ASTM test procedure ASTM E8 for room temperature tests and ASTME21 for elevated temperatures.

Referring to FIGS. 1 and 2, comparison of the Larson-Miller parametersfor the invention alloy A and B test bars pursuant to the invention andthe comparison CompSX, PWA 1484, N5, and CMSX-4 nickel base superalloysis shown. The Larson-Miller parameter, P, is used to compare stressrupture characteristics of the nickel base superalloys shown in FIGS. 1and 2. The Larson-Miller parameter is a time-temperature dependentparameter, P=T(° K.)(20+log t)1000 where T is test temperature and t istime to rupture, widely used to extraplote stress rupture data asdescribed in MECHANICAL METALLURGY, section 3-13, pages 483-486,Copyright 1961, 1976 by McGraw-Hill, Inc. FIGS. 1, 2 and 3 reveal thatthe invention alloy A pursuant to the invention is an improvement overthe CompSX test bars with either a single crystal or equiaxed grainstructure. FIG. 1 also includes several commercially available thirdgeneration single crystal superalloy data points as a reference. It isimportant to point out the data provided on the superalloy systemsincluding PWA 1484, N5, and CMSX-4, represent a fully solutionedmicrostructure obtained by heat treatments that have been optimized overtime to enhance the mechanical properties of those superalloys.

FIG. 3 is a bar graph comparing the stress rupture lives for theinvention alloys A and B pursuant to the invention and the comparisonCompSX nickel base superalloy. It is apparent that the invention alloy Apursuant to the invention exhibited a dramatic increase in stressrupture life compared to the comparison CompSX nickel base superalloyunder all testing conditions shown in FIG. 3.

Referring to FIGS. 4, 5, 6, and 7, the tensile testing data is shown forthe invention alloy A pursuant to the invention and the comparisonCompSX, PWA 1484, N5, and CMSX-4 nickel base superalloys. It is apparentthat the invention alloy A pursuant to the invention is comparable tothe comparison nickel base superalloys in tensile strength (e.g.ultimate tensile strength-UTS and 0.2% yield stress-0.2% YS),elongation, and reduction of area over the temperatures tested (e.g.room temperature to 1100° C.).

The nickel base superalloys pursuant to the invention exhibited reducedcasting scale and reduced non-metallic inclusions as a result of theinclusion of the carbon concentrations of 0.087 weight %. For example,the invention alloy A and B investment cast test bars pursuant to theinvention had reduced casting scale and reduced non-metallic inclusionlevels as compared to the CMSX-4 nickel base superalloy and exhibitedimproved castability from the standpoint that vacuum investment casttest bars pursuant to the invention exhibited less exterior scale ascompared to vacuum investment cast test bars of the comparison CMSX-4nickel base superalloy.

Although the invention has been shown and described with respect todetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and scope of the claimed invention.

1. Nickel base superalloy consisting essentially of, in weight %, about12.5% to about 13.5% Cr, 9.0 to about 9.9% Co, about 4.7 to about 5.1%Ti, about 2.8 to about 3.2% Al, about 2.8 to about 4.3% W, about 1.4 toabout 1.6% Mo, about 2.85 to about 3.1% Ta, about 1.0 to about 6.0% Re,about 0.08 to about 0.11% C, about 0.010 to about 0.015% B, up to about0.15% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Niand incidental impurities.
 2. The superalloy of claim 1 having a Recontent of about 2 to about 4 weight %.
 3. The superalloy of claim 2having an N_(v) value of less than 2.37.
 4. Nickel base superalloyconsisting essentially of, in weight %, about 13.0% Cr, 9.0% Co, about4.9% Ti, about 3.0% Al, about 3.03% W, about 1.5% Mo, about 2.95% Ta,about 3.0% Re, about 0.09% C, about 0.012% B, up to about 0.15% Nb, upto about 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidentalimpurities and an N_(v) of about 2.33.
 5. A turbine airfoil comprisingthe superalloy of claims 1, 2, 3, or
 4. 6. A turbine airfoil of claim 5which is a directionally solidified columnar grain or single crystalcast airfoil.
 7. Nickel base superalloy consisting essentially of, inweight %, about 9.5% to about 14.0% Cr, 7.0 to about 11.0% Co, about 3.0to about 5.0% Ti, about 3.0 to about 4.0% Al, about 3.0 to about 4.0% W,about 1.0 to about 2.5% Mo, about 1.0 to about 4.0% Ta, about 1.0 toabout 6.0% Re, up to about 0.25% C, up to about 0.015% B, up to about1.0% Nb, up to about 0.15% Hf, up to about 0.003% Zr, and balance Ni andincidental impurities.
 8. The superalloy of claim 7 having a Re contentof about 2 to about 4 weight %.
 9. The superalloy of claim 8 having anN_(v) value of less than 2.37.
 10. Nickel base superalloy consistingessentially of, in weight %, about 11.75% Cr, 9.0% Co, about 4.0% Ti,about 3.5% Al, about 3.5% W, about 1.75% Mo, about 2.5% Ta, about 3.0%Re, about 0.09% C, up to about 0.012% B, up to about 0.15% Nb, up toabout 0.15% Hf, up to about 0.003% Zr, and balance Ni and incidentalimpurities and an N_(v) of about 2.33.
 11. A turbine airfoil comprisingthe superalloy of claims 7, 8, 9, or
 10. 12. A turbine airfoil of claim11 which is a single crystal cast airfoil.